As it is known in cryptology, encryption techniques (codification) are used so that data exposed to undesired peeking are usually encrypted so that it is difficult for someone not authorised to see or use them. As it is usual in encryption, the term ‘plaintext’ refers to a text which has not been coded or encrypted and it is usually directly readable, and the terms ‘ciphertext’ or ‘encrypted text’ are used to refer to text which has been coded, encrypted. Experts in this art will also assert that, despite of its name, ‘plaintext’ tries to include not only textual data but also binary data, both as a file, a computer file for instance, as well as serial data transferred, for example, from a communication system such as a satellite, telephone or electronic mail systems among others. They will also assert that the terms ‘encryption’ and ‘enciphering’, ‘encrypted’ and ‘ciphered’, ‘encrypting device’ and ‘ciphering device’, ‘decrypting device’ and ‘decipher device’ have respectively an equivalent meaning within cryptology and can be used without distinction within this report.
It is well known among those with some knowledge in this art that, up to now, a large number of encryption schemes have been used. For the time being, using the encryption devices, among which it can be said some as the “Data Encryption Standard” (“DES”), by the “American National Bureau of Standards”, currently “National Institute of Standards and Technology” (“NBS” or “NIST”) in the United States; the “Fast data encipherment algorithm FEAL” (FEAL) developed later in Japan, IECEJ Technical Report IT 86-33 (1986) and object of U.S. Pat. No. 4,850,019 entitled “Data Randomisation Equipment”; the encryption device in U.S. Pat. No. 5,214,703 entitled “Device for the conversion of a digital block and use of same”; as well as the encryption device in U.S. Pat. No. 5,675,653 entitled “Method and apparatus for digital encryption”, the element or user making use of them, after encryption or enciphering of a plaintext, has always delegated the strength of the invulnerability of the encryption in front of an enemy attack aiming to discover the contents of the ciphertext or the encryption key used, trusting in the organisations, institutions, or experts endorsing its security, as well as the degree of confusion and diffusion of values introduced by the encryption device used in the ciphertext. The user or element encrypting a particular plaintext has no objective security in the degree of confusion and diffusion of values present in a ciphertext that result from the application of the encryption device.
Randomisation of an input block has been previously adduced, as in the device in U.S. Pat. No. 4,850,019 entitled “Data randomisation equipment”, invented by Yokosuka Akihiro Shimizu and Yokohama Shoji Miyaguchi, both from Japan, in which two plaintext encrypting devices are presented. In both cases the randomisation of data which they refer to is done according to the individual 64 bits data block provided as input data, as described in the patent description where it is stated that “final channel data obtained after function and transform operations are combined by combining means to produce randomised data corresponding to the input data.” Properties and features of said randomisation lie in the input data block, in the encryption key, and in the operations and transformations that the device carries out in the 64 bit data block provided as input data. It can also be said that such invention uses a 64 bit encryption key for the first encrypting device, and a 128 bit encryption key for the second.
The encryption device in U.S. Pat. No. 5,214,703 entitled “Device for the conversion of a digital block and use of same”, invented by James L. Massey y Xuejia Lai, both from Switzerland, is another encrypting device that also uses well-known diffusion and confusion techniques, but the ciphertext message that results from its application presents no such properties to allow objective measures, by the user or element using the device, of the degree of confusion and diffusion of values presented in said ciphertext message and, as it happened with the abovementioned device, the confusion and diffusion introduced refer to the 64 bit data block provided as input for encryption. It is said in the description of said patent that “it can be proved that the quantity of four operations is a minimum for meeting the object of diffusion”, and therefore relegating to experts, organisations or institutions, the appraisal of the diffusion and confusion introduced in the ciphertext resulting from its application. Such a device makes use of a 128 bit encryption key.
Another example of encrypting device where a good scramble in the resultant ciphertext is adduced is that one in U.S. Pat. No. 5,675,653 entitled “Method and apparatus for digital encryption”, invented by Nelson Douglas Valmore, Jr. In said patent it is alluded the fact that the experts, people with good knowledge in cryptology, will recognise that typical digital encryption usually use two well-known techniques such as substitution and transposition; but this device does not yield such a ciphertext that it is possible in a useful way for a layperson in each encryption to verify in an objective way the scramble achieved in the resultant ciphertext.
The device in patent application WO-A-99/57845 entitled “Randomization-encryption system”, published the 11 Nov. 1999, occasionally generates as ciphertext randomised text that substantially presents the at random number sequence properties, so that the degree of diffusion and confusion of values in the randomised-encrypted text introduced by the encryption key used can be checked in an objective way. The randomisation of the ciphertext depends on the plaintext that it is encrypted and on the selected encryption key, and such device do not allow to be sure in advance that any encryption key with any plaintext generates such a ciphertext that complies with the at random number sequence properties, and it also forces the person that uses it to the explicit evaluation if he wants to know if there is the maximum degree of diffusion and confusion values. Therefore, in case that the ciphertext does not comply with the at random number sequence properties and later to the explicit evaluation, it is necessary to select a new encryption key to be used and repeat the randomisation-encryption process if he wants the randomised-encrypted text to have the maximum confusion and diffusion properties. This entails the disadvantages inherent in the selection of a different encryption key for a particular plaintext and the increase of different encryption keys with which he can be forced to work. Furthermore, with a large plaintext the probability that the whole resultant encrypted text complies with the at random number sequence properties are lower so that you can have to repeat this process successively.
It is worth mentioning the existence of ciphering devices that operate according to the input data, which can be either the encryption key or the plaintext message data. Some examples of them can be the ciphering device in U.S. Pat. No. 4,157,454 entitled “Method and system for machine enciphering and deciphering”, invented by Wolfram Becker, that shows an enciphering algorithm with rotations depending on the used encryption key, as well as the AMENDED SHEET ciphering device in U.S. Pat. No. 5,724,428 entitled “Block encryption algorithm with data-dependent rotations”, whose inventor is Ronald L. Rivest, and it makes use of rotations according to the input data and intermediate encryption results in order to determine the quantity of each data rotation being encrypted.
The usage of encryption devices by laypeople is becoming very common, as for example in commercial electronic transactions or electronic mail among others. These laypeople would thank if they could always be sure, in an objective way which could be verified by them, that the maximum degree of the diffusion and confusion of the values is present in the encrypted data. The availability of such an encryption system would allow them to have a stronger security in the degree of confidentiality of the encrypted information and, therefore, to use the encryption systems with more confidence; this would help encryption systems to have a larger acceptance with a consequent increase in usage and a worldwide strengthening of data communications, electronic mail and commercial electronic transactions among others.